Reply To: Precise analog voltage measurement using Arduino

Hey Goodluck
Sounds like you have got the measurement traceability going. The local water company here installed a German ultrasonic meter, on the recommendation of Siemens. So far it seems to be slig

Hey Goodluck
Sounds like you have got the measurement traceability going. The local water company here installed a German ultrasonic meter, on the recommendation of Siemens. So far it seems to be slightly under-reading the water flow compared to the impeller meter I have, but haven’t done any detailed measurements on it. I’m waiting to see if there will be any visibility of the readings to customers (me).
I’m using 12V and 4-20mA on a project. Its a using the commercial Onset U30-C3G with analog interface and reporting in over cellular. It has a WiFi option.
The 4-20mA interface has been very good, accurate and stable signal across the 12bit ADC.
I first tested it with some resistors to see how stable it is.

Our issue was accuracy – we wanted to measure changes of 1/100′ or 0.01′. That limited the dynamic range to 10′ depth of water.
So technically the dynamic range is about 10bit- 2**10=1024. Then you need to take into account digital quantization – the accuracy of the ADC and potential slight drifts that can occur. Temperature drift also needed to be accounted for, and potentially there can be a 20C change in temperature across a day/24hr cycle.
I enclose a graph taken from a snapshot of two sensors tied together over 24hrs of pre-deployment testing in a stable 3.6′ water column. Typically I tested in 0.5′ of water, but wanted to test them at different depth. I believe the noise is coming from the sensors – both sensors are the same type of depth gage, but different responses.
The graph demonstrates the value in doing some acceptance testing in known conditions – in this case level water (except for slight evaporation).
You may want to consider how you can generate a 1/16 gallon flow/leak and then monitor the meters over a couple of weeks.

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